I see that NM changed apparently a bunch around there and much more
information is passed in ENV. Not exactly sure if everything, but it
might be worthy to check what all ENV contains while one of those
dispatchers run.

(much more information can be passed reliably than on command line)

I wasn't just able to find some documentation for the dispatcher
scripts... they are a little bit hidden magic :)

I just verified this on my system (with NM 0.8.998 as well on Factory).

$1 still refers to the device (eth0) and $2 to the mode (up/down).
No changes there.